src/Tools/jEdit/src/context_menu.scala

   {
     text_area0 match {
       case text_area: TextArea =>
         text_area.getBuffer match {
           case buffer: Buffer
-          if (JEdit_Lib.buffer_name(buffer).endsWith(".bib")) =>
+          if (JEdit_Lib.buffer_name(buffer).endsWith(".bib") && buffer.isEditable) =>
             val menu = new JMenu("BibTeX entries")
             for (entry <- Bibtex.entries) {
               val item = new JMenuItem(entry.name)
               item.addActionListener(new ActionListener {
                 def actionPerformed(evt: ActionEvent): Unit =